1. Field of the Invention
This invention relates to a process for producing low sulfur content heating fuel from carbonaceous materials, and more particularly to a process for converting high sulfur carbonaceous materials to a low sulfur fuel acceptable as a source of energy in power generation plants not equipped with emission control devices.
2. Description of the Prior Art
Air quality standards as set forth by federal and state laws for power generation plants not provided with sulfur dioxide removal equipment require that the sulfur content of bituminous coal not exceed 0.7%. This corresponds to a sulfur dioxide emission of about 1.1 lb. SO.sub.2 per million B.t.u. of coal. In some areas of the country, the sulfur dioxide emissions are permitted to be as high as 1.8 lb. SO.sub.2 per million B.t.u. of coal.
In the eastern part of the United States where bituminous coal is the major source of fossil fuel, the reserves of bituminous coal with less than 0.7% sulfur are in scarce supply. However, coal reserves with a sulfur content of up to 2.0% are abundant. Therefore, unless expensive sulfur removal equipment is installed at the power plants to permit burning of higher sulfur content coal, a critical shortage of acceptable power plant fuel will occur. The availability of power plant fuel would be greatly increased if coal with a sulfur content of up to 2.0% could be used for power generation in plants without emission control equipment.
Alternative methods of removing sulfur from coal have been proposed, such as sulfur removal gasification and sulfur removal by liquefaction. The major drawback to coal gasification is that the processes must operate at a rate which corresponds to the fuel demand of the power plant. Due to the fact that the power demand for a 24 hour period will fluctuate between offpeak and peak power periods, the processes must be interrupted to meet the variations in power demand resulting in loss of process efficiency.
With regard to sulfur removal by coal gasification, complete gasification of the coal in a two-stage gasification process operated at elevated temperatures and pressures produces a solid, low sulfur fuel and methane rich product gas as disclosed in U.S. Pat. No. 3,746,522. The char product is burned in a boiler to provide steam for power generation and the purified methane rich product gas is available as a synthetic natural gas. Nevertheless, complete gasification of high sulfur coal is not necessary to produce a low sulfur fuel acceptable for power generation in plants without emission control devices. Thus, the conversion of high sulfur coal to a low sulfur fuel as a clean power plant fuel can be substantially improved by only partially gasifying coal at elevated temperatures and atmospheric pressure in which only the most reactive volatile portion of the coal reacts to produce a low sulfur char and a product gas.
There is need to provide a process for converting high sulfur coal to a low sulfur fuel as a source of energy for power generation in which the sulfur is substantially removed from the fuel prior to consumption so that the emissions after consumption comply with air quality standards. The process must operate efficiently at all times and take into account the variations in power demand which occur between peak and offpeak periods.